Conventionally, two adjacent corner portions of a cabinet are assembled with one another by means of spot-welding or separate connectors. However, scars or marks are made on the cabinet members by such welding or connection words, harming the cabinet's appearance. The scars or marks invite an additional work such as painting, which complicates the manufacturing process and results in inefficiency of the manufacturing process, since the additional painting can hardly be done in the same assembly workshop because of space limitations.